Displacement Sensor, Displacement Detecting Device, and Operation Device

ABSTRACT

A displacement sensor having a rectangular shaped elastic member. A piezoelectric element is attached to a first main face of the elastic member. The piezoelectric element has a rectangular-shaped piezoelectric sheet and electrodes on both main faces of the piezoelectric sheet. The piezoelectric sheet is made of poly-L-lactic acid and is at least uniaxially-stretched. The piezoelectric element is attached so that the uniaxial-stretching direction of the piezoelectric sheet is 45° relative to a long-side direction of the elastic member. When the elastic member is bent along the long-side direction, the piezoelectric sheet is stretched along the long-side direction, and the piezoelectric element generates voltage of predetermined level.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of International applicationNo. PCT/JP2012/059443, filed Apr. 6, 2012, which claims priority toJapanese Patent Application Nos. 2011-086412, filed Apr. 8, 2011,2011-101407, filed Apr. 28, 2011, and 2011-106990, filed May 12, 2011,the entire contents of each of which are incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates to a displacement sensor attached to asubject and detecting a bending and a twist in the subject, and adisplacement detecting device and an operation device each using thedisplacement sensor.

BACKGROUND OF THE INVENTION

Various displacement sensors for detecting a bending amount or the likeof a subject by using a sheet-shaped member having piezoelectricity aredevised. For example, Patent Literature 1 describes a sensor fordetecting movement of a columnar projection which moves in the verticaldirections by pulsation, using polyvinylidene fluoride (hereinbelow,called PVDF).

-   Patent Literature 1: Japanese Unexamined Patent Application    Publication No. 2000-41960

SUMMARY OF THE INVENTION

However, as described also in the Patent Literature 1, in thedisplacement sensor using PVDF, since PVDF has pyroelectricity, astructure in which temperature change does not occur in PVDF at the timeof measurement has to be built, so that the configuration of thedisplacement sensor is complicated. Although PVDF reacts susceptibly toa displacement in the molecular orientation direction, it hardly reactsto a displacement in the direction perpendicular to the orientationdirection. There is consequently a problem such that, for example, atwist in which a displacement in the positive direction and adisplacement in the negative direction exist cannot be detected by asingle film.

Therefore, an object of the present invention is to provide adisplacement sensor, a displacement detecting device, and an operationdevice with a simple structure capable of effectively, accurately, andreliably detecting a displacement in a direction in which a bending, atwist, or the like is desired to be detected without depending onmeasurement temperature.

A displacement sensor of the present invention includes: an elasticmember; and a flat-film-shaped piezoelectric element attached to a firstmain face of the elastic member and obtained by forming electrodes onboth main faces of a piezoelectric sheet. In the displacement sensor,preferably, the piezoelectric sheet contains polylactic acid and isstretched at least in a uniaxial direction.

In the configuration, the piezoelectric sheet is displaced by adisplacement in the elastic member and, by the piezoelectric effect, anoutput voltage according to the displacement amount is output from theelectrodes formed on both faces of the piezoelectric sheet. By thevoltage, the displacement in the elastic member can be detected.

The piezoelectric sheet containing polylactic acid has a characteristicthat when the sheet is stretched at least in a uniaxial direction,piezoelectricity in a specific direction becomes very large. Therefore,by disposing the piezoelectric sheet containing polylactic acid on theelastic member so that the uniaxial stretch direction is along apredetermined direction, various displacements can be individually andeffectively detected in accordance with the orientation of the uniaxialstretch direction.

Consequently, when the angle formed between the uniaxial stretchdirection and a direction (predetermined direction) of a displacementdesired to be detected is properly set, displacements (for example, abending, a twist, or the like which will be described later) in thepredetermined direction of the elastic member can be individually andeffectively detected. That is, different from PVDF, polylactic acid hasthe piezoelectricity d₁₄, not d₃₁, so that a displacement in thepiezoelectric sheet can be simply detected and, in addition,displacements in the predetermined direction can be individually andeffectively detected. Since the piezoelectric sheet is made ofpolylactic acid, pyroelectricity which occurs in PVDF does not occur,and the voltage which is output according to the displacement amount isnot influenced by a temperature change.

In the displacement sensor of the invention, as an example, thepiezoelectric sheet is a flat film whose main face has an almostrectangular shape, and can be formed so that a stretch axis of theuniaxial direction is oriented along at least a direction of about 45°or a direction of about −45° with respect to a long-side direction ofthe flat film.

With the configuration, the direction in which the piezoelectricity ofthe piezoelectric sheet is the highest can be matched with the directionof a bending (displacement detection direction) along the long-sidedirection. Consequently, a bending state can be detected, and thelong-side direction in which a bending occurs most becomes thedisplacement detection direction, so that a higher-sensitivitydisplacement sensor can be realized.

In the displacement sensor of the invention, as an example, thepiezoelectric sheet is a flat film whose main face has an almostrectangular shape, and can be formed so that a stretch axis of theuniaxial direction is oriented along at least a direction of about zerodegree or a direction of about 90° with respect to a long-side directionof the flat film.

In the configuration, the direction in which the piezoelectricity of thepiezoelectric sheet is the highest can be matched with the direction ofa twist (displacement detection direction) along the long-side andshort-side directions. Consequently, a high-sensitivity displacementsensor for detecting a twisted state can be realized.

In the displacement sensor of the invention, as an example, thepiezoelectric sheet is a flat film whose main face has an almostrectangular shape, and can be formed so that a stretch axis of theuniaxial direction is oriented along at least a direction of about 22.5°or a direction of about 67.5° with respect to a long-side direction ofthe flat film.

In the configuration, a bending along the long-side direction and atwist in the long-side and short-side directions can be simultaneouslyand effectively detected.

Preferably, the displacement sensor of the invention has the followingconfiguration. The flat-film-shaped piezoelectric element attached tothe first main face of the elastic member is set as a firstflat-film-shaped piezoelectric element. A second flat-film-shapedpiezoelectric element attached to a second main face opposed to thefirst main face of the elastic member, and obtained by formingelectrodes on both main faces of a piezoelectric sheet is furtherprovided. The piezoelectric sheet of the second flat-film-shapedpiezoelectric sheet contains polylactic acid and is formed so as to bestretched at least in a uniaxial direction.

In the configuration, the flat-film-shaped piezoelectric elements areattached to both main faces of the elastic member. By making thepolarities of output voltages of the elements match and simply addingthe voltages, the output voltage can be doubled. Further, the polaritiesof output voltages are made match and an average value process can beperformed. Thus, higher-precision displacement detection can berealized.

In the displacement sensor of the invention, preferably, thepiezoelectric sheet of the first flat-film-shaped piezoelectric elementis a flat film whose main face has an almost rectangular shape, and isformed so that a stretch axis of the uniaxial stretch is oriented alongat least a direction of about 45° or a direction of about −45° withrespect to a long-side direction of the flat film. The piezoelectricsheet of the second flat-film-shaped piezoelectric element is a flatfilm whose main face has an almost rectangular shape, and is formed sothat a stretch axis of the uniaxial direction is oriented along at leasta direction of about zero degree or a direction of about 90° withrespect to a long-side direction of the flat film.

In the configuration, a bending along the long-side direction can bedetected by the first flat-film-shaped piezoelectric element, and atwist in the long-side and short-side directions can be detected by thesecond flat-film-shaped piezoelectric element. That is, a bending and atwist can be simultaneously and individually detected by a singledisplacement sensor.

In the displacement sensor of the invention, preferably, thepiezoelectric sheet of the first flat-film-shaped piezoelectric elementis a flat film whose main face has an almost rectangular shape, and isformed so that a stretch axis of the uniaxial direction is orientedalong at least a direction of about 22.5° or a direction of about 67.5°with respect to a long-side direction of the flat film, and thepiezoelectric sheet of the second flat-film-shaped piezoelectric elementis a flat film whose main face has an almost rectangular shape, and isformed so that a stretch axis of the uniaxial direction is orientedalong at least a direction of about 22.5° or a direction of about 67.5°with respect to a long-side direction of the flat film.

In the configuration, the presence/absence of a displacement and a twicecan be detected by both faces of the elastic member. Therefore, adisplacement and a twist can be detected more accurately.

Preferably, the elastic member of the displacement sensor of theinvention has conductivity, and the electrode on the elastic member sideof the first flat-film-shaped piezoelectric element and the electrode onthe elastic member side of the second flat-film-shaped piezoelectricelement are used also by the elastic member having conductivity.

In the configuration, the electrode on the elastic member side of thefirst flat-film-shaped piezoelectric element and the electrode on theelastic member side of the second flat-film-shaped piezoelectric elementare used also by the elastic member, so that the configuration of thedisplacement sensor is simplified, and can be made thinner.

In the displacement sensor of the invention, a plurality of theflat-film-shaped piezoelectric elements can be stacked.

In the displacement sensor of the invention, a plurality of at least oneof the piezoelectric sheet of the first flat-film-shaped piezoelectricelement or the piezoelectric sheet of the second flat-film-shapedpiezoelectric element can be stacked.

In those configurations, an output voltage can be obtained from each ofthe stacked flat-film-shaped piezoelectric elements, so that the totaloutput voltage of the displacement sensor can be increased.

In the displacement sensor of the invention, preferably, the electrodeand the elastic member are made of material having translucency.

In the configuration, since polylactic acid has high translucency, byforming the other components of material having translucency, adisplacement sensor having translucency can be realized.

The displacement sensor of the invention can be also realized by thefollowing configuration. A displacement sensor includes aflat-film-shaped piezoelectric element attached to a circumferentialface of a columnar shaft as a member to be detected and obtained byforming electrodes on both main faces of a piezoelectric sheet. It ispreferable that the piezoelectric sheet contains polylactic acid and isformed so that a stretch axis is oriented in either a direction of aboutzero degree or in a direction of about 90° with respect to acircumferential direction.

In the configuration, a thin-type displacement sensor capable ofdetecting a twist in a shaft can be realized.

The displacement sensor of the invention can be also realized by thefollowing configuration. A displacement sensor includes first and secondflat-film-shaped piezoelectric elements each obtained by formingelectrodes on both main faces of a piezoelectric sheet. The first andthe second flat-film-shaped piezoelectric elements have the samestrength. The first and second flat-film-shaped piezoelectric elementsare in contact with each other so that their flat plate faces areopposed to each other. Preferably, the piezoelectric sheet containspolylactic acid and is stretched at least in a uniaxial direction.

Also with such a configuration, a displacement in one direction and adisplacement in two directions can be detected as described above.Further, it is unnecessary to use an elastic member, so that theconfiguration of the displacement sensor can be simplified.

According to the present invention, a displacement detecting device canbe realized by using the displacement sensor. The displacement detectingdevice includes: any of the above-described displacement sensors;voltage measuring means which detects generation voltage in thedisplacement sensor; and a capacitor connected in parallel to thedisplacement sensor.

In the configuration, although it is difficult to maintain the outputvoltage level by the displacement almost constant with only thedisplacement sensor, by connecting the capacitor in parallel to thedisplacement sensor, the output voltage level can be maintained almostconstant while the member to be detected displaces. It facilitatesdetection of the output voltage level and, further, detection of adisplacement amount.

The displacement sensor of the invention can be used for the followingoperation device. The operation device includes: a casing which issubject to external force; a displacement sensor which detectsdisplacements in a bending direction and a twist direction individuallywhen the casing is deformed by external force; and an applicationexecuting unit which executes a predetermined application by using adetection voltage of the displacement sensor according to the externalforce.

In the configuration, by using the detection voltage of the displacementsensor, a predetermined application can be executed. The casing can beused also an elastic member.

Particularly, when displacements in the bending direction and the twistdirection can be detected individually, an application according to thedetection voltage in the bending direction and an application accordingto the detection voltage in the twist direction can be separatelyexecuted.

In the operation device of the invention, preferably, the applicationexecuting unit includes: a communication control unit which transmitsthe detection voltage by radio; and a program executing unit whichreceives a radio signal from the communication control unit and uses thedetection voltage for a program execution status of the application.

In the case of realizing the configuration as a separate member, it isunnecessary to integrate the displacement detection part and theapplication executing unit. Consequently, even when the applicationexecuting unit becomes bigger, the displacement detection part can bemade smaller and thinner. Therefore, for example, even when thedisplacement detecting function is provided in a product worn by theuser (such as shoes) and a product which is held and operated by a hand(such as a controller, a remote controller, or the like), the size ofthose products is not increased.

In the operation device of the invention, preferably, the displacementsensor has a flat-film-shaped piezoelectric element obtained by formingelectrodes on both main faces of a piezoelectric sheet, and outputs adetection voltage of the flat-film-shaped piezoelectric elementaccording to a displacement.

In the configuration, a concrete structure of the displacement sensorused for the operation device is shown. By using the structure, thedisplacement sensor can be made thinner. Thus, the operation devicessuch as a controller and a remote controller can be configured thinly.

In the operation device of the invention, preferably, the piezoelectricsheet contains polylactic acid and is stretched at least in a uniaxialdirection.

In the configuration, since the piezoelectric sheet contains polylacticacid, the detection voltage according to the displacement can be madehigh, and a change in the detection voltage value according totemperature can be also suppressed.

In the operation device of the invention, preferably, a photovoltaicelement is disposed in the casing.

In the configuration, even when a general chemical-reaction-type batterysuch as a nickel battery is not provided, a control signal for theoperation device according to the detection voltage can be output.

In the operation device of the invention, preferably, theflat-plate-shaped elastic member has a double-layer structure, and aphotovoltaic element having a flat plate shape is disposed between anelastic member of an upper layer and an elastic member of a lower layer.The elastic member on a wave-receiving-face side of the photovoltaicelement and the flat-film-shaped piezoelectric element can havetranslucency.

In the configuration, while having the photovoltaic element, reductionin thickness and size can be realized. Since the photovoltaic elementserves as the displacement neutral layer, high-precision displacementdetection can be realized in a state where the stress ofextension/contraction related to the photovoltaic element is minimized.

Preferably, the operation device of the invention further includes asecondary battery for charging electromotive force generated by thephotovoltaic element.

In the configuration, the electromotive force of the photovoltaicelement can be charged. Consequently, even in the case where theelectromotive force of the photovoltaic element is low and a situationthat no electromotive force can be generated, a control signal for theoperation device according to the detection voltage can be output.

In the operation device of the invention, preferably, the photovoltaicelement has a charging function part which is connected to an outputterminal of the flat-film-shaped piezoelectric element and charges thesecondary battery by using the detection voltage of the flat-film-shapedpiezoelectric element.

In the configuration, while the flat-film-shaped piezoelectric elementuses the detection voltage for generation of a control signal for theoperation device, the secondary battery can be charged by the detectionvoltage.

Preferably, the operation device of the invention has the followingconfiguration. The operation device includes a flat-film-shapedpiezoelectric element and a casing. The flat-film-shaped piezoelectricelement has a piezoelectric sheet containing polylactic acid andstretched at least in a uniaxial direction, and electrodes formed onboth main faces of the piezoelectric sheet. The casing has facesextended in two directions which are almost orthogonal to each other inplan view. A region in which the electrodes of the flat-film-shapedpiezoelectric element are opposed to each other is disposed in aposition where the difference of distortions in the two directions whichare almost orthogonal to each other is large when the planes extended inthe two directions which are almost orthogonal to each other in thecasing are deformed.

In the configuration, for the deformation of the planes extended in thetwo directions which are almost orthogonal to each other in the casing,the flat-film-shaped piezoelectric element generates chargesefficiently. Thus, the output voltage sensitivity to deformation in thecasing can be improved.

In the operation device of the invention, the piezoelectric sheet may bedisposed only in the region in which the electrodes of theflat-film-shaped piezoelectric element are opposed.

In the operation device of the invention, the electrodes of theflat-film-shaped piezoelectric element may be formed in regions exceptfor the center of planes extending in the two directions which arealmost orthogonal to each other in the casing.

In the configurations, examples of disposing the flat-film-shapedpiezoelectric element in the casing are described.

In the operation device of the invention, preferably, the electrodes areformed in a region in which polarities of charge distributions generatedby distortion of the casing are the same.

In the configuration, cancellation of charges in the electrodes does notoccur, so that the charges caused by a deformation can be generated moreefficiently. As a result, the output voltage sensitivity to adeformation can be further improved.

In the operation device of the invention, the electrode is made of aplurality of partial electrodes, and the plurality of partial electrodesmay be connected so that polarities of voltages generated match and areadded.

In the configuration, the voltages generated by the plurality of partialelectrodes can be added without being cancelled out. Therefore, theoutput voltage sensitivity to a deformation can be further improved.

Further, an operation device of the invention may have the followingconfiguration. The operation device includes a flat-film-shapedpiezoelectric element and a touch panel part. The flat-film-shapedpiezoelectric element has a piezoelectric sheet containing polylacticacid and stretched at least in a uniaxial direction, and press forcedetecting electrodes formed on both main faces of the piezoelectricsheet. The touch panel part is stacked so as to be parallel to theflat-film-shaped piezoelectric element.

In the configuration, a press position can be detected by the touchpanel part and a press force can be detected by the flat-film-shapedpiezoelectric element. Therefore, control according to the pressposition and the press force can be performed.

According to the present invention, with the simple and thin structure,a displacement desired to be detected such as a bending or a twist canbe efficiently, accurately, and reliably detected without depending onmeasurement temperature.

BRIEF EXPLANATION OF THE DRAWINGS

FIG. 1 is an appearance perspective view of a displacement sensor 10according to a first embodiment.

FIGS. 2A and 2B are a plan view and a side view, respectively, of thedisplacement sensor 10.

FIG. 3 is a diagram illustrating the relations among an applied electricfield direction, a stretch direction, and a stretch state of apiezoelectric sheet using PLLA.

FIG. 4A is a diagram illustrating an almost side face shape of thedisplacement sensor 10 in a state where a bending displacement is zero,and FIG. 4B is a diagram illustrating an almost side face shape of thedisplacement sensor 10 in a state where a predetermined bendingdisplacement occurs.

FIG. 5 is an equivalent circuit diagram of a displacement detectingdevice 100 including the displacement sensor 10.

FIGS. 6A and 6B illustrate output characteristics of the displacementdetecting device 100.

FIGS. 7A, 7B, and 7C are a plan view, a side view, and a rear view,respectively, of a displacement sensor 10A according to a secondembodiment.

FIGS. 8A and 8B are a plan view and a side view, respectively, of adisplacement sensor 10B according to a third embodiment.

FIGS. 9A, 9B, and 9C are a plan view, a side view, and a rear view,respectively, of a displacement sensor 10C according to a fourthembodiment.

FIGS. 10A and 10B are diagrams illustrating shapes in an almostperspective view of a displacement sensor in a state where a twistdisplacement is zero and in a state where a predetermined twistdisplacement occurs.

FIG. 11 is a diagram illustrating a state where a displacement sensor10D according to a fifth embodiment is attached to a shaft 22.

FIGS. 12A and 12B are diagrams illustrating a schematic configuration ofa game controller 201 using the displacement sensor 10C.

FIGS. 13A and 13B are diagrams illustrating a state where the gamecontroller 201 is curved and a state where the game controller 201 istwisted, respectively.

FIG. 14 is a diagram illustrating a schematic configuration of a shoe300 with a monitoring function using the displacement sensor 10C.

FIGS. 15A and 15B are diagrams illustrating a schematic configuration ofa remote controller 401 using the displacement sensor.

FIGS. 16A and 16B are diagrams illustrating a schematic configuration ofa touch panel sensor 501 using the displacement sensor.

FIG. 17 is a side sectional view of a remote controller 401A havinganother configuration.

FIGS. 18A and 18B are diagrams illustrating a schematic configuration ofa displacement sensor made of a material having no piezoelectricity andthe concept of displacement detection.

FIG. 19 is a plan view illustrating a mode of mounting a displacementsensor for detecting a twist in a plate-shaped device.

FIGS. 20A and 20B are diagrams illustrating disposition of apiezoelectric element 30 in an operation device 801.

FIG. 21 is a distribution diagram of a distortion rate DrX in thelong-side direction (X direction) of a casing 810 in the case where thecenter of a surface wall 812F of the casing 810 having a rectangularshape is pressed.

FIG. 22 is a distribution diagram of a distortion rate DrY in theshort-side direction (Y direction) of the casing 810 in the case wherethe center of the surface wall 812F of the casing 810 having arectangular shape is pressed.

FIG. 23 is a distribution diagram of a distortion difference DrXY in thecase where the center of the surface wall 812F of the casing 810 havinga rectangular shape is pressed.

FIGS. 24A to 24F are diagrams illustrating examples of disposition ofthe piezoelectric element 30 in the casing 810.

FIG. 25 is a plan view of the casing 810, illustrating an example ofadhering a piezoelectric sheet 380 in an almost entire face of thecasing 810.

FIG. 26 is a plan view of the casing 810, illustrating an example ofadhering the piezoelectric sheet 380 in an almost entire face of thecasing 810 and forming a plurality of electrodes.

DETAILED DESCRIPTION OF THE INVENTION

A displacement sensor according to a first embodiment of the presentinvention will be described with reference to the drawings. FIG. 1 is anappearance perspective view of a displacement sensor 10 of theembodiment. FIGS. 2A and 2B are a plan view and a side view,respectively, of the displacement sensor 10. FIG. 2B is a side view inwhich the long-side direction of the displacement sensor 10 correspondsto the lateral direction of the diagram (an end face of the short-sidedirection is viewed).

The displacement sensor 10 has an elastic member 20 having a flat plateshape and a piezoelectric element 30 in a flat film shape. The elasticmember 20 has predetermined thickness and, in plan view, a rectangularshape having long and short directions, which is long in one directionand short in a direction perpendicular to the direction. The elasticmember 20 is made of polymer having relatively high strength such aspolyethylene terephthalate (PET) or acrylic resin (PMMA). In this case,preferably, the thickness of the elastic member 20 is, for example,about 0.5 mm to 2 mm. It is sufficient that the mechanical strength ofthe elastic member 20 is higher than at least that of a piezoelectricsheet 300 as a component of the piezoelectric element 30.

The piezoelectric element 30 has the piezoelectric sheet 300 having arectangular shape similar to that of the elastic member 20. Thepiezoelectric sheet 300 is made of poly-L-lactic acid (hereinbelow,called PLLA). The piezoelectric sheet 300 may be made of poly-D-lacticacid (hereinbelow, called PDLA).

An electrode 301 is formed on an almost entire first main face of thepiezoelectric sheet 300. An electrode 302 is formed on an almost entiresecond main face of the piezoelectric sheet 300. As the electrodes 301and 302, preferably, any of an organic electrode whose main componentsare ITO, ZnO, and polythiophene or an organic electrode whose maincomponent is polyaniline is used. By using those materials, theelectrodes 301 and 302 have high translucency. Consequently, thedisplacement sensor having high translucency can be realized.

It is more preferable to use any of an organic electrode whose maincomponent is polythiophene or an organic electrode whose main componentis polyaniline as the electrodes 301 and 302 for the reason that theelectrode has translucency and, in addition, breakage of the electrodecaused by bending hardly occurs. In the case where translucency isunnecessary, the electrodes 301 and 302 may be formed by a metal coatingformed by vapor deposition or plating or a printed electrode film madeby a silver paste. In particular, an aluminum vapor-deposited film issuitable since it can be formed at low cost.

An external connection terminal 41 is connected to the electrode 301,and an external connection terminal 42 is connected to the electrode302.

PLLA used for the piezoelectric sheet 300 of the displacement sensor 10having such a configuration is chiral polymer and the main chain has ahelical structure. The PLLA sheet is uniaxially-stretched. Whenmolecules are oriented, the PLLA sheet has piezoelectricity. Thepiezoelectric constant of the uniaxially-stretched PLLA is very high inthe category of high polymers.

The multiple number of stretch is suitably about three to eight times.By performing heat treatment after the stretch, crystallization ofstretched-chain crystal of polylactic acid is accelerated, and thepiezoelectric constant improves. In the case of performing biaxialstretching, by making the multiple numbers of stretch of the axesdifferent from each other, an effect similar to that in the case ofuniaxial stretching can be obtained. For example, in the case ofperforming stretching of eight times in a direction which is set as an Xaxis and performing stretching of twice in a Y-axis direction orthogonalto the X axis, with respect to the piezoelectric constant, an effectequivalent to the case of performing uniaxial stretching of four timesin the X-axis direction is obtained. Since a uniaxially-stretched filmis simply easily split in the stretch axis direction, by performingbiaxial stretching as described above, the strength can be increased tosome extent.

PLLA comes to have piezoelectricity only by the stretch, and does notneed poling process unlike other polymers such as PVDF or piezoelectricceramics. That is, the piezoelectricity of PLLA which does not belong toferroelectrics is not brought about by polarization of ions unlikeferroelectrics such as PVDF and PZT but is derived from the spiralstructure as the characteristic structure of molecules. Consequently,pyroelectricity which occurs in other ferroelectric piezoelectricelements does not occur in PLLA. Further, in PVDF and the like,fluctuations occur with time in the piezoelectric constant and, in somecases, the piezoelectric constant decreases remarkably. However, thepiezoelectric constant of PLLA is extremely stable with time.

As described above, when PLLA is used, it is not influenced bypyroelectricity. Therefore, at the time of detection, without dependingon the temperature in a detection position, output voltage accordingonly to the displacement amount can be obtained. Since PLLA is a polymerand has flexibility, it is not damaged by a large displacement unlikepiezoelectric ceramics. Therefore, even when a displacement amount islarge, the displacement amount can be detected with reliability.

The relative permittivity of PLLA is about 2.5 and very low. When d isset as a piezoelectric constant and ∈^(T) is set as dielectric constant,a piezoelectric output constant (=piezoelectric “g” constant, g=d/∈^(T))becomes a large value.

The piezoelectric “g” constant of PVDF having dielectric constant ∈₃₃^(T)=13×∈₀ and piezoelectric constant d₃₁=25 pC/N is g₃₁=0.2172 Vm/Nfrom the above-described equation. On the other hand, when thepiezoelectric “g” constant of PLLA having piezoelectric constant d₁₄=10pC/N is converted to g₃₁, since d₁₄=2×d₃₁, d₃₁=5 pC/N, and thepiezoelectric “g” constant becomes g₃₁=0.2258 Vm/N. Therefore, by PLLAhaving the piezoelectric constant d₁₄=10 pC/N, sufficient sensorsensitivity equivalent to that of PVDF can be obtained. The inventors ofthe present invention obtained PLLA of d₁₄=15 to 20 pC/N experimentally.By using the PLLA sheet, a sensor having very high sensitivity isrealized.

Further, since the piezoelectricity of PLLA has anisotropy, a sheet iscutout from a uniaxially-stretched original sheet as will be describedbelow. FIG. 3 is a diagram illustrating the relations among an appliedelectric field direction, a stretch direction, and a stretch state of apiezoelectric sheet using PLLA. To facilitate explanation, in this case,a case where a piezoelectric sheet 390 before application of electricfield has a square shape is illustrated.

The piezoelectric sheet having a square shape illustrated by a brokenline 390 in FIG. 3 is uniaxially stretched in a direction indicated byan arrow symbol 901 in FIG. 3 (lateral direction in FIG. 3). When anelectric field in a direction indicated by an electric field symbol 911in FIG. 3 (a direction to the depth in the drawing from this side ofFIG. 3) is applied to the piezoelectric sheet 390, by the effect of d₁₄,the sheet is deformed to a parallelogram indicated by a solid line 392.At this time, the direction in which the piezoelectric sheet isstretched the most is a direction turned by 45° from the uniaxialstretch direction in a counterclockwise fashion, and the direction inwhich the piezoelectric sheet becomes the shortest is a direction turnedby −45° from the uniaxial stretch direction in a counterclockwisefashion.

Therefore, as illustrated by an alternate long and two short dashes line391 in FIG. 3, a piezoelectric sheet is cut out using, as the long-sidedirection, the 45° direction from the uniaxial stretch direction. Insuch a manner, the above-described piezoelectric sheet 300 can be formedin a state where sensitivity is highest to stretch.

The piezoelectric sheet 300 of the embodiment is formed so that theuniaxial stretch direction forms an angle of 45° from the long-sidedirection. The piezoelectric element 30 obtained by forming theelectrodes 301 and 302 on both faces of the piezoelectric sheet 300having such a shape as described above is attached to the first mainface of the elastic member 20 by a not-illustrated translucent adhesive.

The angle is not limited to exactly 45° but may be about 45°. The angleof “about 45°” refers to an angle, for example, in a range of about ±10°of 45°. The angles are design matters to be properly determinedaccording to a general design including bending sensing precision on thebasis of the use of the displacement sensor.

The displacement sensor 10 having such a shape can detect a bendingalong the long-side direction of 45° from the uniaxial stretch directionas illustrated in FIG. 4B. FIG. 4A is a diagram illustrating an almostside face shape of the displacement sensor in a state where a bendingdisplacement is zero, and FIG. 4B is a diagram illustrating an almostside face shape of the displacement sensor 10 in a state where apredetermined bending displacement occurs.

In the case where the bending displacement is zero, that is, in the casewhere a force of causing bending is not applied from the outside to thedisplacement sensor 10, the elastic member 20 is in a state where itsmain face is flat as illustrated by a symbol 10ST in FIG. 4A. In thiscase, the piezoelectric element 30 is not stretched, and no voltage isgenerated.

In the case where the bending displacement has a predetermined value,that is, in the case where a force of causing bending is applied fromthe outside to the displacement sensor 10, the elastic member 20 is in astate where it is curved along the long-side direction of the main faceas illustrated by a symbol 10CS in FIG. 4B. In this case, thepiezoelectric element 30 is stretched along the long-side direction inaccordance with a bending amount. As a result, a voltage according tothe stretch amount is generated between the electrodes 301 and 302 ofthe piezoelectric element 30. By detecting the voltage, the stretch inthe piezoelectric element 30, that is, the bending amount of thedisplacement sensor 10 can be detected.

As described above, by using the configuration of the embodiment, thebending amount can be detected. Further, a circuit as illustrated inFIG. 5 may be configured. FIG. 5 is an equivalent circuit diagram of adisplacement detecting device 100 including the displacement sensor 10.FIGS. 6A and 6B illustrate output characteristics of the displacementdetecting device 100. FIG. 6A illustrates an output voltage change fromoccurrence of a displacement until cancellation of the displacement, andFIG. 6B illustrates a displacement-voltage characteristic.

As illustrated in FIG. 5, one of the external connection terminals ofthe displacement sensor 10 is connected to a variable control terminalof a variable resistor VR. The variable resistor VR is connected betweenconstant resistors R1 and R2, a drive voltage Vcc is applied to an endon the constant resistor R1 side of a series circuit of the constantresistors R1 and R2 and the variable resistor VR, and an end on theconstant resistor R2 side is connected to the ground.

The other external connection terminal of the displacement sensor 10 isconnected to a non-inversion input terminal of an operational amplifierOP. A DC voltage detector 101 is connected to the output terminal of theoperational amplifier OP. The output terminal of the operationalamplifier OP is feed-back connected to the inversion input terminal ofthe operational amplifier OP. Also to the operational amplifier OP, thedrive voltage Vcc is supplied.

Further, to the displacement sensor 10, a capacitor Co is connected inparallel. In this case, as the capacitor Co having capacity of, forexample, about 0.2 μF is used.

By using the displacement detecting device 100 having such aconfiguration, the output voltage of the displacement sensor 10 can bealmost maintained while displacement occurs as illustrated in FIG. 6A.In the displacement sensor 10 itself, voltage is generated at the timingthe displacement occurs, and the output voltage value decreases rapidlydue to unintended leak current or the like. However, by connecting thecapacitor Co in parallel to the displacement sensor 10, the timeconstant of the voltage drop can be made longer. As a result, the outputvoltage can be detected more reliably.

By using the configuration of the embodiment, as illustrated in FIG. 6B,the output voltage value changes almost linearly relative to thedisplacement amount. Therefore, the displacement amount can be detectedaccurately.

Since the input impedance of the operational amplifier OP is very large,the time constant at the time of voltage drop can be made long withoutusing the capacitor Co. Therefore, the capacitor Co may not be used.

As described above, by using the displacement sensor 10 and thedisplacement detecting device 100 of the embodiment, the bending amountalong a predetermined direction (in the embodiment, the long-sidedirection) can be detected with high accuracy and high sensitivity.Further, since the piezoelectricity of PLLA has anisotropy, in theconfiguration of the embodiment, only the bending (stretch) in thelong-side direction is detected. Consequently, without being influencedby bending or twist in a direction different from the long-sidedirection as a detection direction, only bending in the long-sidedirection as the detection direction can be detected accurately.

Next, a displacement sensor according to a second embodiment will bedescribed with reference to the drawings. FIGS. 7A, 7B, and 7C are aplan view, a side view, and a rear view, respectively, of a displacementsensor 10A according to the second embodiment.

The displacement sensor 10A of the embodiment has the elastic member 20,a first piezoelectric element 31 corresponding to a firstflat-film-shaped piezoelectric element of the present invention, and asecond piezoelectric element 32 corresponding to a secondflat-film-shaped piezoelectric element of the invention. The elasticmember 20 is the same as that of the first embodiment, and itsdescription will not be therefore repeated.

The first piezoelectric element 31 is attached to the first main face ofthe elastic member 20. The first piezoelectric element 31 has apiezoelectric sheet 310 having a rectangular shape. Like thepiezoelectric sheet 300 of the first embodiment, the piezoelectric sheet310 is formed so that 45° is formed between the uniaxial stretchdirection and the long-side direction. Electrodes 311 and 312 are formedalmost entirely on both faces of the piezoelectric sheet 310. Anexternal connection terminal 41A is connected to the electrode 311, andan external connection terminal 42A is connected to the electrode 312.

The second piezoelectric element 32 is attached to the second main faceopposed to the first main face of the elastic member 20. The secondpiezoelectric element 32 has a piezoelectric sheet 320 having arectangular shape. Like the piezoelectric sheet 310 and thepiezoelectric sheet 300 of the first embodiment, the piezoelectric sheet320 is also formed so that 45° is formed between the uniaxial stretchdirection and the long-side direction. Electrodes 321 and 322 are formedalmost entirely on both faces of the piezoelectric sheet 320. Anexternal connection terminal 41B is connected to the electrode 321, andan external connection terminal 42B is connected to the electrode 322.

The first and second piezoelectric elements 31 and 32 are attached tothe elastic member 20 so that the uniaxial stretch direction forms 90°when viewed from a direction orthogonal to the main face of the elasticmember 20.

With such a configuration, for example, in the case where a bendingoccurs such that the piezoelectric sheet 310 of the first piezoelectricelement 31 extends in the long-side direction, the piezoelectric sheet320 of the second piezoelectric element 32 contracts. When the first andsecond piezoelectric elements 31 and 32 are formed of the same materialand in the same shape, the neutral face of the bending becomes thecenter axis in the thickness direction of the elastic member 20.Consequently, the absolute value of the force of extending the firstpiezoelectric element 31 and that of the force of contracting the secondpiezoelectric element 32 become equal to each other. Thus, voltageshaving the same absolute value and opposite characteristics aregenerated in the first and second piezoelectric elements 31 and 32.

Therefore, by a pattern of connecting the external connection terminalsor the like, by adding the output voltage of the first piezoelectricelement 31 and the output voltage of the second piezoelectric element 32while making the characteristics (positive and negative) match, anoutput voltage which is twice as large as that in the case of using onepiezoelectric element described in the first embodiment can be obtained.By performing an average value process while making the characteristics(positive and negative) of the output voltage of the first piezoelectricelement 31 and the output voltage of the second piezoelectric element 32match, an output voltage with a small error can be obtained.

Although 90° is formed between the uniaxial stretch direction of thepiezoelectric sheet 310 of the first piezoelectric element 31 and theuniaxial stretch direction of the piezoelectric sheet 320 of the secondpiezoelectric element 32 when seen from a direction perpendicular to themain face in the embodiment, the first and second piezoelectric elements31 and 32 may be attached so that the directions are parallel to eachother. In this case, the first and second piezoelectric elements 31 and32 can obtain output voltages of the same characteristic.

Next, a displacement sensor according to a third embodiment will bedescribed with reference to the drawings. FIGS. 8A and 8B are a planview and a side view, respectively, of a displacement sensor 10B of thethird embodiment.

The displacement sensor 10B has an elastic member 21 havingconductivity. Like the elastic member 20 described in the foregoingembodiments, the elastic member 21 has a long rectangular shape. Theelastic member 21 may be formed of, for example, metal or obtained bymetal-plating the surface of an insulating elastic member (PET, PMMA, orthe like). The elastic member 21 is connected to the ground (isgrounded).

A piezoelectric sheet 330 is attached to the first main face of theelastic member 21. The piezoelectric sheet 330 has the same material,the same shape, and the same uniaxial stretch direction as those of thepiezoelectric sheet 310 of the second embodiment. An electrode 331 isformed on a surface opposed to the elastic member 21 of thepiezoelectric sheet 330. The external connection terminal 41A isconnected to the electrode 331. By the piezoelectric sheet 330 and theelectrode 331 and the conductive elastic member 21 disposed whilesandwiching the piezoelectric sheet 330, a third piezoelectric element33 (corresponding to a first flat-film-shaped piezoelectric element ofthe present invention) is constructed.

A piezoelectric sheet 340 is attached to the second main face opposed tothe first main face of the elastic member 21. The piezoelectric sheet340 has the same material, the same shape, and the same uniaxial stretchdirection as those of the piezoelectric sheet 320 of the secondembodiment. An electrode 341 is formed on a surface opposed to theelastic member 21 of the piezoelectric sheet 340. The externalconnection terminal 41B is connected to the electrode 341. By thepiezoelectric sheet 340 and the electrode 341 and the conductive elasticmember 21 disposed while sandwiching the piezoelectric sheet 340, afourth piezoelectric element 34 (corresponding to a secondflat-film-shaped piezoelectric element of the present invention) isconstructed.

Also with such a configuration, in a manner similar to the foregoingsecond embodiment, a displacement caused by a bending in a long-sidedirection can be detected. Further, with the configuration of the thirdembodiment, the conductive elastic member 21 also serves as theelectrode of one of the two piezoelectric elements. Therefore, theconfiguration of the displacement sensor 10B is simplified and noise dueto an external factor can be further suppressed.

Next, a displacement sensor according to a fourth embodiment will bedescribed with reference to the drawings. FIGS. 9A, 9B, and 9C are aplan view, a side view, and a rear view, respectively, of a displacementsensor 10C according to the fourth embodiment.

The displacement sensor 10C of the embodiment has the elastic member 20,a fifth piezoelectric element 35 corresponding to the firstflat-film-shaped piezoelectric element of the present invention, and asixth piezoelectric element 36 corresponding to a secondflat-film-shaped piezoelectric element of the invention. The elasticmember 20 is the same as that of the first embodiment and itsdescription will not be repeated.

The fifth piezoelectric element 35 is attached to the first main face ofthe elastic member 20. The fifth piezoelectric element 35 has apiezoelectric sheet 350 having a rectangular shape. Like thepiezoelectric sheet 300 of the first embodiment, the piezoelectric sheet350 is formed so that 45° is formed between the uniaxial stretchdirection and the long-side direction. Electrodes 351 and 352 are formedalmost entirely on both faces of the piezoelectric sheet 350. Theexternal connection terminal 41A is connected to the electrode 351, andthe external connection terminal 42A is connected to the electrode 352.

The sixth piezoelectric element 36 is attached to the second main faceopposed to the first main face of the elastic member 20. The sixthpiezoelectric element 36 has a piezoelectric sheet 360 having arectangular shape. The piezoelectric sheet 360 is formed so that theuniaxial stretch direction and the long-side direction are parallel toeach other (the angle formed=zero degree).

The angle is not limited to exactly zero degree but may be about zerodegree. The angle of “about zero degree” refers to an angle, forexample, in a range of about ±10° of zero degree. The angles are designmatters to be properly determined according to a general designincluding bending sensing precision on the basis of the use of thedisplacement sensor.

Electrodes 361 and 362 are formed almost entirely on both main faces ofthe piezoelectric sheet 360. The external connection terminal 41B isconnected to the electrode 361, and the external connection terminal 42Bis connected to the electrode 362.

The fifth and sixth piezoelectric elements 35 and 36 are attached to theelastic member 20 so that 45° is formed between the uniaxial stretchdirection of the piezoelectric sheet 350 and the uniaxial stretchdirection of the piezoelectric sheet 360, and the long-side direction(=the uniaxial stretch direction) of the piezoelectric sheet 360 isparallel to the long-side direction of the elastic member 20.

FIG. 10A is a diagram illustrating the shape in an almost perspectiveview of a displacement sensor in which only the sixth piezoelectricelement 36 is disposed in a state where a twist displacement is zero,and FIG. 10B illustrates the shape in an almost perspective view of thedisplacement sensor in which only the sixth piezoelectric element 36 isdisposed in a state where a predetermined twist displacement occurs.FIGS. 10A and 10B illustrates the displacement sensor in which only thesixth piezoelectric element 36 is disposed in the elastic member 20 tofacilitate explanation of the diagrams and the principle. The principlecan be applied also to the shape illustrated in FIGS. 9A to 9C. FIGS.10A and 10B illustrate the case where the end side AB as one ends in thelong-side direction of the elastic member 20 are defined as the fixedend side, and a twist occurs in the end side CD as the other end. Inother words, they illustrate the case where corners A and B at both endsof the fixed end side AB are fixed corners, and corners C and D at bothends of the end side CD are displaced in directions almost perpendicularto the main face of the elastic member 20 and in directions opposite toeach other.

In the case where a twist displacement is zero, that is, in the casewhere a force of causing a twist is not applied from the outside to theelastic member 20, the elastic member 20 is in a state where the mainface is flat as illustrated by symbol 10STt in FIG. 10A. In this case,the sixth piezoelectric element 36 does not extend/contract, and novoltage is generated across the electrodes on the both faces of thesixth piezoelectric element 36.

In the case where a twist displacement has a predetermined value, thatis, in the case where a force of causing a twist is not applied from theoutside to the elastic member 20 and the end side CD opposed to thefixed end side AB of the elastic member 20 is twisted, the elasticmember 20 is in a state where the corners C and D opposed to the fixedcorners A and B are apart by predetermined distances in directionsperpendicular to the main face (flat face) as compared with the statewhere the corners C and D opposed to the fixed corners A and B are flatas illustrated by symbol 10TOt in FIG. 10B. In this case, the corners Cand D move in directions opposite to each other using the main face as areference.

In this case, the sixth piezoelectric element 36 extends in thedirection of 45° relative to the uniaxial stretch direction at andaround the corner D and contracts in the direction of −45° relative tothe uniaxial stretch direction at and around the corner C. Therefore,contraction/extension (refer to the arrows in solid line in FIG. 10B)occurs along the directions of −45° and +45° relative to the uniaxialstretch direction of the piezoelectric sheet 300 as a component of thesixth piezoelectric element 36, so that a voltage according to theamount of contraction/extension is generated across the electrodes ascomponents in the sixth piezoelectric element 36. By detecting thevoltage, the twist amount of the displacement sensor can be detected.

In the configuration, since the corners C and D are displaced by theequal amount in the directions opposite to each other, the voltagegenerated by the bending is cancelled out. Therefore, only the twistamount can be separated and detected at high precision.

As described above, by using the embodiment, the displacement of thebending is detected by the fifth piezoelectric element 35 attached tothe first main face of the elastic member 20, and the displacement ofthe twist can be detected by the sixth piezoelectric element 36 attachedto the second main face. The displacement of the bending and thedisplacement of the twist can be simultaneously and independentlydetected.

In the embodiment, the uniaxial stretch direction of the sixthpiezoelectric element 36 for detecting a twist and the long-sidedirection of the elastic member 20 are parallel to each other.Alternatively, the sixth piezoelectric element 36 may be formed so thatthe uniaxial stretch direction of the sixth piezoelectric element 36 isperpendicular to the long-side direction, that is, in parallel to theshort-side direction.

To the embodiment, the configuration of commonly using the electrode onthe elastic member side described in the third embodiment can be alsoemployed. In this case, the thin-type displacement sensor having asimplified configuration, resistive to noise due to external factors andcapable of simultaneously detecting a bending and a twist can berealized.

Further, in the case of detecting only a twist as illustrated in FIGS.10A and 10B, it is sufficient to form only the sixth piezoelectricelement 36 in the elastic member 20.

In the configuration of disposing the piezoelectric elements fordetecting displacements in the same direction on both main faces of theelastic member described in the second embodiment and the configurationof disposing the piezoelectric elements for detecting displacements indifferent directions on both main faces of the elastic member describedin the fourth embodiment, when the strengths of the piezoelectricelements disposed on both main faces are the same, the elastic membermay not be provided. In this case, the configuration of the displacementsensor can be simplified, and the thickness can be further reduced.However, to improve sensitivity of detection of a displacement, it ispreferable to provide the elastic member.

In the case where it is sufficient to detect the presence/absence of adisplacement which occurs in the displacement sensor withoutdiscriminating a bending and a twist, the angle formed between thelong-side direction of the elastic member and the uniaxial stretchdirection may be set to an angle other than 0°, 45°, and 90°. In thiscase, preferably, the angle formed between the long-side direction andthe uniaxial stretch direction is set to about 22.5° and about 67.5°.Also in the case of setting the angle formed between the long-sidedirection of the elastic member and the uniaxial stretch direction to arange of about ±10° of 22.5° or a range of about ±10° of 67.5° on thebasis of the use of the displacement sensor and in accordance with thedesign of the entire sensor, similar effects are obtained. In this case,the presence/absence of a displacement caused by the bending and thepresence/absence of a displacement caused by a twist can be alsodetected by a single piezoelectric sheet of PLLA. Although the presenceof a bending and a twist can be detected by a single sheet, by providingthe piezoelectric elements on both faces of the elastic member, theoutput voltage can be doubled, and an average value of two outputvoltages can be obtained. Consequently, the presence of a bending and atwist can be detected more accurately.

By using polylactic acid and performing uniaxial stretch, variousdisplacements can be freely and effectively detected in accordance withthe orientation of the uniaxial stretch direction. Consequently, whenthe angle between the uniaxial stretch direction and the direction of adisplacement desired to be detected (predetermined direction) isproperly set, a displacement (for example, the bending, a twist, or thelike) in a predetermined direction of the elastic member can beeffectively detected. Specifically, since piezoelectricity of polylacticacid has anisotropy, not only a displacement in a piezoelectric sheetcan be detected but also a displacement in a predetermined direction canbe effectively detected.

In the foregoing embodiments, the configurations of detecting adisplacement which occurs in the plate-shaped elastic member 20 havebeen described. As will be described in the following embodiment, adisplacement in objects other than a flat plate can be also detected.

A displacement sensor according to a fifth embodiment will be describedwith reference to the drawings. FIG. 11 is a diagram illustrating astate where a displacement sensor 10D of the embodiment is attached to ashaft 22.

The shaft 22 as an object to be detected has a columnar shape androtates about its center axis (the center point of a circle in asection) as rotation center.

A piezoelectric element 37 as the displacement sensor 10D is attached toa circumferential face of the shaft 22.

The piezoelectric element 37 has a piezoelectric sheet 370 which is longand has a rectangular shape in a state where it is not attached to theshaft. The piezoelectric sheet 370 is formed so that its long-sidedirection is parallel to the uniaxial stretch direction. Electrodes 371and 372 are formed on both main faces of the piezoelectric sheet 370.The electrodes 371 and 372 are connected to not-illustrated externalconnection terminals.

The piezoelectric element 37 having such a shape is attached so that itslong-side direction coincides with the circumferential direction of theshaft 22. As a result, the uniaxial stretch direction (arrow symbol 903in FIG. 11) and the circumferential direction coincide with each other.Although the length in the long-side direction of the piezoelectricelement 37 may be shorter than that of the circumference of the shaft22, preferably, the lengths are equal. The piezoelectric element 37 isadhered to the shaft 22 by an insulating adhesive. Preferably, thestrength after fixation of the insulating adhesive is equal to or higherthan that of the piezoelectric sheet 370 of the piezoelectric element37.

With such a configuration, when a twist occurs in the shaft 22, thepiezoelectric sheet 370 extends in a diagonal line direction, and thepiezoelectric element 37 generates an output voltage according to theextension amount. Accordingly, the twist in the shaft 22 can bedetected.

Although a single-layered piezoelectric element obtained by formingelectrodes on both faces of a single piezoelectric sheet is used in eachof the foregoing embodiments, a piezoelectric element obtained bystacking a plurality of single-layered piezoelectric elements may bealso used. By using the structure in which a plurality of single-layersare stacked, an output voltage can be improved.

Although not described in detail in each of the foregoing embodiments,an insulating protection film may be formed so as to cover the surfaceof each piezoelectric element. In this case, a protection film whoseYoung's modulus is lower than that of the piezoelectric sheet as acomponent of the piezoelectric element is used. Further, it issufficient to design so that a neutral point of a bending or a twistdoes not lie in the piezoelectric element by attachment of theprotection film.

The displacement sensor having a flat film shape is used for thefollowing various operation devices.

(i) Case of Game Operation Input Device (Game Controller)

FIGS. 12A and 12B are diagrams illustrating a schematic configuration ofa game controller 201 using the displacement sensor. FIG. 12A is a planview, and FIG. 12B is a side sectional view. FIG. 13A illustrates astate where the game controller 201 is curved and FIG. 13B illustrates astate where the game controller 201 is twisted. In FIG. 13, theoperation input buttons 220 and 230 are omitted, and a shape thereof issimplified.

The game controller 201 has a casing 210 having an almost rectangularshape. A plurality of operation input buttons 220 and 230 are disposedon the surface wall of the casing 210. The casing 210 has a space 211.In the space 211, operation detectors (not illustrated) for theoperation input buttons 220 and 230 and a communication controller (notillustrated) for controlling communication with an external game machinebody are provided.

On the space 211 side on the rear face wall of the casing 210, thedisplacement sensor 10C described in the fourth embodiment is disposed.The displacement sensor 10C is disposed so that its long-side directionalmost coincides with the long-side direction of the casing 210.

The casing 210 is formed of a material which has predeterminedelasticity and can be curved or twisted by the user.

To the casing 210 of the game controller 201 having such a structure,the user applies an external force so that, as illustrated by symbol 910in FIG. 13A, the center in the long-side direction is displaced towardthe surface side, and both ends in the long-side direction are displacedtoward the rear face side. Consequently, the piezoelectric elementhaving a flat film shape in each of the casing 210 and the displacementsensor 10C is curved along the long-side direction as illustrated bysymbol 911C in FIG. 13A. As described above, the displacement sensor 10Cdetects such a curve in the long-side direction and generates detectionvoltage.

The not-illustrated communication controller obtains the detectionvoltage and transmits a command according to the detection voltage tothe game machine body (corresponding to a “program executing unit” inthe present invention). Accordingly, in the game machine, a processaccording to the controller bending operation of the user can beexecuted by a game program.

Subsequently, the user applies an external force to the casing 210 ofthe game controller 201 as illustrated by symbol 920 in FIG. 13B so thatboth ends in the long-side direction of the game controller 201 areturned in directions opposite to each other using the axis extending thecenter in the short-side direction, along the long-side direction of thegame controller 201 as a reference axis. By the operation, each of thepiezoelectric elements having a flat film shape of the casing 210 andthe displacement sensor 10C contracts along one diagonal line andextends along the other diagonal line as illustrated by symbol 921 t inFIG. 13B. As described above, the displacement sensor 10C detects such atwist and generates a detection voltage.

The not-illustrated communication controller obtains the detectionvoltage and transmits a command according to the detection voltage tothe game machine body. Accordingly, in the game machine, a processaccording to the controller twisting operation of the user can beexecuted by a game program.

In this case, since the displacement sensor 10C uses PLLA as thepiezoelectric sheet as described above, there is no pyroelectricity.Even when the user holds the game controller 201 and heat is conductedto the displacement sensor 10C, no influence is exerted on the detectionvoltage. Therefore, execution of an application in which the bendingoperation and the twist operation are accurately reflected can berealized.

Although the displacement sensor (provided in the game controller) andthe application executing unit (game machine body) are providedseparately, they may be also integrated.

Although the game controller has been described as an example, a similarconfiguration can be applied also to other portable operation inputdevices (such as remote controllers for various AV devices), and similareffects can be obtained. The operation for making a displacement occurin the displacement sensor is not limited to bending and twisting butmay be any operation which can apply an external force to thedisplacement sensor such as touching, pressing, and vibrating.

(ii) Case of Wearable Item (Shoe) with Monitoring Function

FIG. 14 is a diagram illustrating a schematic configuration of a shoe301 with a monitoring function using the above-described displacementsensor. In the shoe 301 with the monitoring function, the displacementsensor 10C is buried in a sole 311 of a shoe body 310. The displacementsensor 10C is disposed so that its main surface is almost parallel tothe rear face of a foot 400 of the user, that is, the surface of thesole 311. Although FIG. 14 illustrates the example of disposing thedisplacement sensor 10C around the base of the toes, the displacementsensor 10C may be disposed around the arch of the foot, the heel, or thelike. Obviously, the displacement sensors 10C may be disposed in aplurality of places.

The displacement sensor 10C is connected to a communication control unit131 via a wiring line 135 also disposed in the sole 311. Thecommunication control unit 131 is constructed by, for example, amicroprocessor, and power is supplied from a battery 132 via a powersupply line 134. The communication control unit 131 transmits adetection voltage based on the bending or twist of the displacementsensor 10C to an external display device or the like (corresponding to a“program executing unit” of the present invention).

With such a configuration, in the case where the user walks, jogs, orthe like, the tilt of the bottom of each of the shoes at the time oflanding and a ground striking posture of the user can be detected by thedisplacement sensor 10C. Consequently, a walking condition and a runningcondition of the user can be accurately detected and can be used for,for example, correction of a walking form or a jogging form of the user.

By employing the displacement sensor 10C using the flat-film-shapedPLLA, without increasing the thickness of the sole, the weight can bedecreased as compared with the case of using a conventional ceramicpiezoelectric member (PZT). In addition, since PLLA has flexibility, bymaking the electrodes formed on the surface of an organic materialhaving flexibility similar to that of PLLA, the sensor is not broken byload or impact from the foot at the time of jogging or walking. SincePLLA is used, the environment load can be also lessened.

Although FIG. 13 illustrates the mode of burying the displacement sensor10C in the sole 311 of the shoe body 310, a mode of burying thedisplacement sensor 10C in a detachable inner sole may be also employed.

The program executing unit is not limited to an external display deviceor the like. It is also possible to provide a pedometer, a voicegenerator, and the like in a shoe, and execute a program using adetection voltage of the displacement sensor.

In the application examples of (i) and (ii), the cases each using thedisplacement sensor capable of individually detecting a bending and atwist have been described. In the case of detecting one of a bending anda twist or in the case of detecting only the presence/absence of abending and a twist, the displacement sensor described in the otherembodiment can be also used.

(iii) Case of Remote Controller

FIGS. 15A and 15B are diagrams illustrating a schematic configuration ofa remote controller 401 using the displacement sensor. FIG. 15A is anappearance perspective view and FIG. 15B is a cross section of A-A′ ofFIG. 15A.

As the basic structure, the remote controller 401 uses the structure ofthe displacement sensor 10C described in the fourth embodiment.Therefore, only a schematic structure will be described.

A flat-film-shaped piezoelectric element 431 is disposed on a first mainface of a flat-plate-shaped elastic member 420 made of transparentacrylic or the like. The piezoelectric element 431 has aflat-film-shaped piezoelectric sheet 4310 made of PLLA, and electrodes4311 and 4312 are formed on both opposed main faces of the piezoelectricsheet 4310.

A flat-film-shaped piezoelectric element 432 is disposed on a secondmain face of the elastic member 420. The piezoelectric element 432 has aflat-film-shaped piezoelectric sheet 4320 made of PLLA, and electrodes4321 and 4322 are formed on both opposed main faces of the piezoelectricsheet 4320.

A control circuit part 410 is formed so as to be connected to theelectrodes of the composite structure having such a configuration. Thecontrol circuit part 410 is formed, for example, on the surface of theelectrode 4311 as a component of the piezoelectric element 431 via anot-illustrated insulator layer. The control circuit part 410 has abattery, the above-described voltage detection circuit, and atransmission controller for transmitting a signal to an external deviceby infrared rays.

The elastic member 420, the piezoelectric elements 431 and 432, and thecontrol circuit part 410 are entirely covered with an insulatingprotection layer 440.

With such a structure, only by simply bending or twisting the body ofthe remote controller 401, various control signals according to thebending and twisting can be transmitted. Concretely, in the case ofemploying a television apparatus (TV apparatus) as the applicationexecution unit of the operation device and using the remote controller401 as a remote controller provided to the TV apparatus, for example, adetection voltage generated by a bending is used for a control signalfor switching channels, and a detection voltage generated by a twist canbe used for a control signal for adjusting volumes.

More concretely, for example, settings are made as follows. When theremote controller 401 is bent so that the piezoelectric element 431 sideextends and the piezoelectric element 432 side contracts, the channel isincremented by one (+1). When the remote controller 401 is bent so thatthe piezoelectric element 431 side contracts and the piezoelectricelement 432 side extends, the channel is decremented by one (−1). In thecase where one end in the long-side direction is twisted clockwise andthe other end is twisted counterclockwise, the volume is increased byone (+1). In the case where one end in the long-side direction istwisted counterclockwise and the other end is twisted clockwise, thevolume is decreased by one (+1). It is also possible to vary theaddition amount and the subtraction amount of channels and volumes inaccordance with the bending amount and the twisting amount.

Since the displacement sensor of the remote controller 401 having theabove-described structure can output a detection voltage of the voltagelevel according to a pressing force and press time, channel continuousswitching speed and increase/decrease of the volume adjustment amountcan be also adjusted according to a pressing force and press time.

Further, a combination of detection voltages according to a bending anda twist can be used as a control signal for controlling power supply.

More concretely, settings are made as follows. In the case ofcontinuously performing bending and twisting when the power of the TVapparatus is in an off state, the power is turned on. In the case ofcontinuously performing the above-described two kinds of twists when thepower of the TV apparatus is in an on state, the power is turned off.

With the above-described configuration, the user can perform the powersupply control, channel switching, and volume adjustment only by thesensation of a hand without recognizing the position of a button in aconventional manner. Therefore, elderly people and visually impairedpeople (for example, who listens to only sound of a TV program) can alsoeasily perform the power supply control, channel switching, and volumeadjustment.

Since no buttons are necessary, the degree of freedom in designing ofthe remote controller improves. Further, when the color is transparent,a more innovative remote controller can be realized. For example, aremote controller which is fashionable and has a neo-futuristic imagecan be realized.

By using a button battery or a polymer battery as the battery used forthe control circuit part 410, the control circuit part 410 can beminiaturized, and deterioration in design of the remote controller canbe suppressed.

Although a TV apparatus is used as an example in the application example(iii), the invention can be applied also to a remote controller of anyof other AV devices such as a magnetic recording/reproducing device, anoptical disk recording/reproducing device, and an audio player.

(iv) Case of Touch Panel Sensor

FIGS. 16A and 16B are diagrams illustrating a schematic configuration ofa touch panel sensor 501 using the above-described displacement sensor.FIG. 16A is an appearance perspective view, and FIG. 16B is a crosssection of B-B′ of FIG. 16A.

The touch panel sensor 501 has a structure in which a touch panel part511 having a flat plate shape and a piezoelectric element 512 having aflat plate shape are stacked so that their flat plate faces (main faces)are parallel to each other.

The piezoelectric element 512 has a flat-film-shaped piezoelectric sheet5120 made of PLLA. Press force detecting electrodes 5121 and 5122 areformed on both opposed main faces of the piezoelectric sheet 5120.

On the surface of the press force detecting electrode 5121 of thepiezoelectric element 512 (the face on the side opposite to thepiezoelectric sheet 5120), an insulating layer 513 made of an elasticmaterial is stacked.

On the face on the side opposite to the piezoelectric element 512 of theinsulating layer 513, the touch panel part 511 is stacked. The touchpanel part 511 has a base material layer 5110 made of dielectric havingpredetermined dielectric constant, and capacitance detecting electrodes5111 and 5112 are formed on both main faces of the base material layer5110. The surface of the capacitance detecting electrode 5112 of thetouch panel part 511 (the face on the side opposite to the base materiallayer 5110) is in contact with the insulating layer 513.

An insulative protection layer 514 is stacked on the surface of thecapacitance detecting electrode 5111 (the face on the side opposite tothe base material layer 5110) of the touch panel part 511.

With such a structure, the touch panel sensor 501 using the insulativeprotection layer 514 side as the user interface side is configured.

In the case where a press force is applied from the outside, the flatplate face (main face) of the touch panel sensor 501 is curved to adegree that it is not easily visibly recognized. Therefore, thepiezoelectric sheet 5120 of the piezoelectric element 512 is alsocurved, and the piezoelectric element 512 can output a detection voltageaccording to the curve amount, that is, the press force. Consequently,by using the touch panel sensor 501, the operation position (pressposition) is detected and the press force can be also simultaneouslydetected.

Therefore, by using the touch panel sensor 501 for remote controllers ofvarious AV devices, control according to a press position and a pressforce can be performed. For example, in the case where a volumeadjustment position is pressed, the volume adjustment speed can bechanged according to the press force. When a fast-forward or rewindoperation position is pressed, control of performing fast-forwarding orrewinding operation at a speed according to the press force can beperformed.

Although the example of using the touch panel part 511 as the userinterface side has been described in (iv), in the case where the touchpanel part 511 is a resistive touch panel, the piezoelectric element 512may be used as the user interface side.

In a mode of using the flat-film-shaped displacement sensor for variousoperation devices, the structure illustrated in FIG. 17 can be used fordevices such as the game controller 201, the remote controller 401, andthe touch panel sensor 501 which are used in a condition that they areirradiated with sunlight or other light waves having a wavelengthsimilar to that of the sunlight. FIG. 17 is a side sectional view of aremote controller 401A having a solar battery 450. Although a remotecontroller is illustrated as an example in FIG. 17, the configuration ofFIG. 17 can be used for other operation input devices such as a gamecontroller and a touch panel sensor.

The remote controller 401A illustrated in FIG. 17 has the sameconfiguration as that of the remote controller 401 illustrated in FIG.15 except that a stack body of an elastic member 420U, the solar battery450, and an elastic member 420D is used in place of the elastic member420.

Each of the elastic members 420U and 420D has a flat film shape and ismade of, for example, acrylic resin. Preferably, the elastic member onthe wave receiving face side of the solar battery 450 is made of amaterial having high translucency.

The solar battery 450 has a flat film shape and is made of a materialhaving flexibility. The solar battery 450 is sandwiched between theelastic members 420U and 420D so that the flat faces match. Although asolar battery is used, a flat-film-shaped device having a charging unit(secondary battery) capable of receiving light waves, generatingelectromotive force, and charging the generated electromotive force maybe also used.

The flat-film-shaped piezoelectric element 431 is disposed on the faceon the side opposite to the solar battery 450 in the elastic member420U. The flat-film-shaped piezoelectric element 432 is disposed on theface on the side opposite to the solar battery 450 in the elastic member420D.

The complex stack body in which the piezoelectric element 432, theelastic member 420D, the solar battery 450, the elastic member 420U, andthe piezoelectric element 431 are stacked in this order is covered witha protection layer 440A.

With such a configuration, a control signal can be generated by theelectromotive force generated by the solar battery 450 which receivessunlight and power from the secondary battery charged with theelectromotive force. In such a manner, a remote controller which doesnot have a general chemical-reaction-type battery such as a nickelbattery can be realized. Obviously, a chemical-reaction-type battery(button cell) or the like can be also provided. By also providing achemical-reaction-type battery, also in the case where charging of thesolar battery is insufficient, a control signal can be output.

Although the configuration of sandwiching the solar battery 350 betweenthe elastic members 420U and 420D has been described, the solar battery350 may be disposed on the surface side of the remote controller 401A.With a configuration of sandwiching the solar battery 350 between theelastic members 420U and 420D, the layer of the solar battery 350 can beused as a neutral layer of a bending and a twist, so that a displacementcan be detected more reliably. Although the solar battery 350 isdisposed on the entire face in plan view of the remote controller 401Ain the above-described configuration, it can be also partly disposed.

A function unit for connecting the secondary battery and an electrodefor outputting detection voltage of the piezoelectric element andcharging the secondary battery with a part of the detection voltage maybe also provided. When such a function unit is provided, in the casewhere detection voltage equal to or higher than the voltage levelsufficient to generate a control signal of the remote controller 401A isobtained, an excess voltage amount can be charged to the secondarybattery. Particularly, in the mode of disposing the piezoelectric sheets4311 and 4321 of the piezoelectric elements 431 and 432 on almost entirefaces of the flat-film-shaped elastic members 420U and 420D, thedetection voltage can be made larger, and it is suitable for theconfiguration in which the secondary battery can be charged. It is morepreferable to use PLLA for the piezoelectric sheets as described above.

In a very preferable mode in each of the foregoing embodiments, thepiezoelectric element in which the piezoelectric sheet is made of PLLAis used as the displacement sensor. From the viewpoint of detecting abending or a twist and using it for a control signal, a displacementsensor made of any of other materials having piezoelectricity and adisplacement sensor made of a material having no piezoelectricity to bedescribed below can be also used.

The other materials having piezoelectricity include a material usingpiezoelectric constant d₁₄ and a material using piezoelectric constantd₃₁.

(A) The following materials use the piezoelectric constant d₁₄.

poly-γ-methyl-L-glutamate

poly-γ-benzyl-L-glutamate

cellulose

collagen

poly-D-propylene oxide

PDLA (poly-D-lactic acid)

With those materials using the piezoelectric constant d₁₄, thedisplacement sensors and various devices can be realized with astructure similar to that of the piezoelectric element using PLLAdescribed above.

(B) Materials using the piezoelectric constant d₃₁ include the followingpoled polymers, ferroelectric polymers, and inorganic materials.

<Poled Polymers>

nylon 11

polyvinyl fluoride

polyvinyl chloride

vinylidene cyanide-vinyl acetate copolymer

poly uric acid

<Ferroelectric Polymers>

polyvinylidene fluoride

vinylidene fluoride-trifluoroethylene copolymer

<Inorganic Materials>

barium titanate (BaTiO₃)

crystal (SiO₂)

lead zirconate titanate (PZT)

zinc oxide (ZnO)

(C) Displacement Sensor Made of Material Having No Piezoelectricity

FIGS. 18A and 18B are diagrams illustrating a schematic configuration ofa displacement sensor 60 made of a material having no piezoelectricityand the concept of displacement detection. FIG. 18A is a plan view ofthe displacement sensor 60, and FIG. 18B is an enlarged view forexplaining the displacement detection concept.

As illustrated in FIG. 18A, the displacement sensor 60 has an elasticmember 601 and a displacement detection electrode 602. The elasticmember 601 is made by a polymer film or the like, has a flat film shape,and has insulation property.

The displacement detection electrode 602 is formed on one of the mainfaces of the elastic member 601. The displacement detection electrode602 has a meander electrode and a lead electrode for connecting themeander electrode to the outside. When a displacement of the elasticmember 601 occurs along the long-side direction of the elastic member601, in the displacement detection electrode 602, a plurality ofstraight parts in the meander electrode become longer as shown in FIG.18B. Specifically, each of the straight parts in the meander electrode,having length Lo along the long-side direction of the elastic member 601before a displacement occurs along the long-side direction in theelastic member 601 changes to length Ls (>Lo). Accordingly, each of thestraight parts in the meander electrode is also narrowed. Therefore, theresistance value of the meander electrode of the displacement detectionelectrode 602 changes according to a displacement. By detecting thechange in the resistance value, the displacement of an object whosedisplacement is to be detected can be detected.

In the case of using displacement sensors in the groups (B) and (C), itis sufficient to properly install a displacement sensor in accordancewith a direction of detection to a displacement detection object (abending direction or a twist direction). For example, in the case ofdetecting a twist in a flat-plate-shaped device (such as the remotecontroller) as a displacement detection object, it is sufficient to usethe configuration as illustrated in FIG. 19. FIG. 19 is a plan viewillustrating a mode of mounting a displacement sensor for detecting atwist in a plate-shaped device.

As illustrated in FIG. 19, a device 701 having a flat plate shape has arectangular main body 720 having a flat plate shape (flat film shape),and rectangular piezoelectric elements 731A and 731B each having a flatfilm shape. The main body 720 is made of a material which is twisted byan external force, such as an elastic member. The piezoelectric elements731A and 731B are disposed on the main face of the main body 720 so thatdisplacement sensitivity to a twist in the main body 720 becomes higher.For example, concretely, in the case of FIG. 19, the piezoelectricelements 731A and 731B are disposed on the main body 720 so that thelong-side direction of the piezoelectric elements 731A and 731B and thelong-side direction of the main body 720 form an angle of about 45° whenviewed from the direction orthogonal to the main face of the main body720. The piezoelectric elements 731A and 731B are disposed on the mainbody 720 so that their long-side directions form an angle of about 90°.

With such a configuration, the displacement sensor in the groups (B) and(C) can realize a device (a remote controller or the like) for detectinga specific direction (bending or twist) and outputting a control signalaccording to the detected direction. The displacement sensors of PLLAand in the group (A) can be attached with the structure as illustratedin FIG. 19.

In the case of disposing a piezoelectric element in a casing to form anoperation device like the game controller, the following mode can bealso used. FIGS. 20A and 20B are diagrams illustrating disposition ofthe piezoelectric element 30 in an operation device 801. FIG. 20A is aplan view of the operation device 801, and FIG. 20B is a cross sectionof A-A′ of FIG. 20A. In FIGS. 20A and 20B, only a casing 810 and thepiezoelectric element 30 are illustrated. The other components of theoperation device 801 are not illustrated.

The casing 810 has a rectangular parallelepiped shape which is long inone direction (hereinbelow, the direction will be called a long-sidedirection) and is short in a direction (hereinbelow, the direction willbe called a short-side direction) orthogonal to the long-side direction.The casing 810 has a structure in which a surface wall 812F and a rearface wall 812R are opposed to each other over a gap. Long-side-directionside walls 821 and 822 and short-side-direction side walls 823 and 824are formed along the outer periphery of the surface wall 812F and theouter periphery of the rear face wall 812R. With the structure, thecasing 810 has an internal space 811. In the internal space 811, thepiezoelectric element 30 is disposed together with not-illustratedvarious components of the operation device 801.

The piezoelectric element 30 is the same as the piezoelectric element 30used for the displacement sensor 10 in the first embodiment.

Concretely, the piezoelectric element 30 has the rectangularpiezoelectric sheet 300 having a flat film shape. The piezoelectricsheet 300 is made of PLLA. Although PLLA is used here, another materialmay be used as long as it has piezoelectric constant d14 and whosepiezoelectricity has anisotropy. The piezoelectric sheet 300 is formedso that the uniaxial stretch direction forms an angle of 45° withrespect to the long-side direction of the piezoelectric sheet 300.

The electrode 301 is formed on an almost entire first main face of thepiezoelectric sheet 300. The electrode 302 is formed on an almost entiresecond main face of the piezoelectric sheet 300. As the material of theelectrodes 301 and 302, any of the materials described in the firstembodiment may be used. For example, any of an organic electrode whosemain components are ITO, ZnO, and polythiophene, an organic electrodewhose main component is polyaniline, a metal coated film formed by vapordeposition or plating, and a printed electrode film formed by silverpaste may be used.

The flat-film-shaped piezoelectric element 30 having such a structure isdisposed in an almost center in the long-side direction and near an endin the short-side direction in plan view of the casing 810. In theexample of FIGS. 20A and 20B, the piezoelectric element 30 is disposedin a position near a center part of the long-side-direction side wall821 and is in contact with the long-side-direction side wall 821 in therear face wall 812R. In this case, the piezoelectric element 30 isdisposed so that the side face in the long-side direction of thepiezoelectric element 30 is in contact with the long-side-direction sidewall 821. In other words, the piezoelectric element 30 is disposed inthe casing 810 so that the long-side direction of the piezoelectricelement 30 and that of the casing 810 almost coincide with each other.

By employing such a disposition structure of the piezoelectric element30, a press in the surface wall 812F or the rear face wall 812R of thecasing 810 can be efficiently detected by the following principle.

FIG. 21 is a distribution diagram of a distortion rate DrX in thelong-side direction (X direction) of the casing 810 in the case wherethe center of the surface wall 812F of the casing 810 having arectangular shape is pressed.

FIG. 22 is a distribution diagram of a distortion rate DrY in theshort-side direction (Y direction) of the casing 810 in the case wherethe center of the surface wall 812F of the casing 810 having arectangular shape is pressed. FIG. 23 is a distribution diagram of adistortion difference DrXY in the case where the center of the surfacewall 812F of the casing 810 having a rectangular shape is pressed. Thedistortion difference DrXY is calculated by the difference between thedistortion rate DrX in the long-side direction and the distortion rateDrY in the short-side direction. In FIGS. 21, 22, and 23, X0 correspondsto an intermediate part of the long-side-direction side walls 821 and822 in FIG. 20. X1 corresponds to an end on the short-side-directionside wall 823 side of the long-side-direction side walls 821 and 822 inFIG. 20. X2 corresponds to an end on the short-side-direction side wall824 side of the long-side-direction side walls 821 and 822 in FIG. 20.Y0 corresponds to an intermediate part of the short-side-direction sidewalls 823 and 824 in FIG. 20. Y1 corresponds to an end on thelong-side-direction side wall 821 side of the short-side-direction sidewalls 823 and 824 in FIG. 20. Y2 corresponds to an end on thelong-side-direction side wall 822 side of the short-side-direction sidewalls 823 and 824 in FIG. 20.

As illustrated in FIGS. 21 and 22, in the case of pressing the center ofthe surface wall 812F of the casing 810, the distortion rate DrX in thelong-side direction and the distortion rate DrY in the short-sidedirection change according to positions. Concretely, they change asfollows.

Distortion Rate DrX in Long-Side Direction (Refer to FIG. 21)

The distortion rate DrX in the long-side direction increases toward the“+” direction toward the center of the surface wall 812F regardless ofthe long-side and short-side directions. In regions close to thelong-side-direction side walls 821 and 822, the distortion rate DrX inthe long-side direction has a value close to “0” regardless of theposition along the long-side direction. In this case, the distortionrate DrX is slightly “+” in the center in the long-side direction.

The distortion rate DrX in the long-side direction largely changes alongthe long-side direction in the center in the short-side direction.Concretely, it becomes largely “+” around the center and largely “−” atboth ends (parts which are in contact with the short-side-direction sidewalls 823 and 824).

The distortion rate DrX in the long-side direction is “0” at thecorners.

Distortion rate DrY in short-side direction (refer to FIG. 22)

The distortion rate DrY in the short-side direction increases toward the“+” direction toward the center of the surface wall 812F regardless ofthe long-side and short-side directions. In regions close to theshort-side-direction side walls 823 and 824, the distortion rate DrY inthe short-side direction has a value close to “0” regardless of theposition along the short-side direction. In this case, the distortionrate DrY is slightly “+” in the center in the short-side direction.

The distortion rate DrY in the short-side direction largely changesalong the short-side direction in the center in the long-side direction.Concretely, it becomes largely “+” around the center and largely “−” atboth ends (parts which are in contact with the long-side-direction sidewalls 821 and 822).

The distortion rate DrY in the short-side direction is “0” at thecorners.

Therefore, as illustrated in FIG. 23, the distortion difference DrXYbecomes almost “0” in the center of the surface wall 812F regardless ofthe long-side and short-side directions. The distortion difference DrXYbecomes largely “+” in positions around the center in the long-sidedirection of the long-side-direction side walls 821 and 822 and close tothe long-side-direction side walls 821 and 822. The distortiondifference DrXY becomes largely “−” in positions around the center inthe short-side direction of the short-side-direction side walls 823 and824 and close to the short-side-direction side walls 823 and 824.

Since the piezoelectric sheet 300 of the piezoelectric element 30 hasthe piezoelectric constant d14, when the piezoelectric element 30 isdisposed in the casing 810 so that the uniaxial stretch direction of thepiezoelectric sheet 300 (the piezoelectric element 30) and the long-sideand short-side directions of the casing 810 form an angle of 45°, bydisposing the element in a region where the absolute value of thedistortion difference DrXY is the largest, the voltage according to thepress amount becomes high.

FIGS. 24A to 24F are diagrams illustrating examples of disposition ofthe piezoelectric element 30 in the casing 810. FIGS. 24A to 24Fillustrate examples of disposing the piezoelectric elements 30 havingthe same shape in the casings 810 having the same shape. In FIGS. 24A to24F, the point O denotes the center of the casing 810 in plan view. Ineach of the diagrams, the amount of charges generated by thepiezoelectric element 30 in the case of pressing the point O from thesurface wall 812F side is shown.

FIGS. 24A to 24F illustrate the case of using the casing 810 whoselength in the long-side direction is 80 mm and whose length in theshort-side direction is 60 mm, and the piezoelectric sheet 300 made ofPLLA whose length in the long-side direction is 30 mm and whose lengthin the short-side direction is 10 mm. The amount of charges is indicatedin the case of pressing the surface wall 812F with 1 kgf.

FIGS. 24A, 24B, and 24C illustrate the case where the long-sidedirection of the piezoelectric element 30 and that of the casing 810 arealmost parallel to each other.

In the case of FIG. 24A, the piezoelectric element 30 is disposed in thecenter in the short-side direction of the casing 810 and in anintermediate position between the center of the long-side direction ofthe casing 810 and the short-side-direction side wall 823. In this case,the charge amount is +4.3 nC.

In the case of FIG. 24B, the piezoelectric element 30 is disposed in thecenter of the casing 810. In this case, the charge amount is +1.8 nC.

In the case of FIG. 24C, the piezoelectric element 30 is disposed in thecenter in the long-side direction of the casing 810 and in a positionwhere it is in contact with the long-side-direction side wall 821 (endin the short-side direction). In this case, the charge amount is +7.0nC. FIGS. 24D, 24E, and 24F illustrate the case where the long-sidedirection of the piezoelectric element 30 and that of the casing 810 arealmost perpendicular to each other.

In the case of FIG. 24D, the piezoelectric element 30 is disposed in thecenter in the long-side direction of the casing 810 and between thecenter point O and the long-side-direction side wall 821. In this case,the charge amount is −4.0 nC.

In the case of FIG. 24E, the piezoelectric element 30 is disposed in thecenter of the casing 810. In this case, the charge amount is +0.61 nC.

In the case of FIG. 24F, the piezoelectric element 30 is disposed in thecenter in the short-side direction of the casing 810 and in a positionwhere it is in contact with the short-side-direction side wall 823 (endin the long-side direction). In this case, the charge amount is +3.8 nC.

It is understood from the above that, in the case of disposing thepiezoelectric element 30 in the casing 810, by disposing thepiezoelectric element 30 in a region where the absolute value of thedistortion difference DrXY is the largest, the charge amount having alarger absolute value can be obtained.

Therefore, as described above and as illustrated in FIG. 20, bydisposing the piezoelectric element 30 in the casing 810, the outputvoltage sensitivity to pressing (displacement) can be improved.Accordingly, even when the size of the piezoelectric element 30 isregulated, the operation device having high sensitivity to the pressingoperation can be realized.

The disposition mode illustrated in FIG. 20 is just an example. Anotherdisposition mode may be used as long as the piezoelectric element 30 isdisposed in a region where the absolute value of the distortiondifference is large. In the case where regions of different signs (“+”and “−”) mixedly exist in the region in which the piezoelectric element30 is disposed, charges generated in the regions are cancelled out, sothat the generation charge amount of the piezoelectric element 30becomes smaller. Therefore, in the region in which the piezoelectricelement 30 is disposed, preferably, the piezoelectric element 30 isdisposed in the casing 810 so that charges (voltages) of the same signare generated as possible, in other words, so that the polarities ofcharge distributions become the same.

Although FIG. 20 illustrates the example of disposing the piezoelectricelement 30 in the region where the distortion difference is large. It isalso possible to dispose the piezoelectric sheet entirely on the insideof the rear face wall 812R of the casing 810 and form an electrode onlyin the region where the distortion difference is large.

FIG. 25 is a plan view of the casing 810, illustrating an example ofadhering a piezoelectric sheet 380 in an almost entire face of thecasing 810. The piezoelectric element 38 has the piezoelectric sheet 380disposed in an almost entire face of an internal space in plan view ofthe casing 810 and an electrode 381 formed in a predetermined region inthe piezoelectric sheet 380. On the face on the side opposite to theelectrode 381 of the piezoelectric sheet 380, another electrode isformed so as to be opposed to the electrode 381.

The piezoelectric sheet 380 is formed so that the long-side directionand the short-side direction and the uniaxial stretch direction form anangle of about 45°.

The electrode 381 is formed in a shape in which the electrode widthgradually increases along the long-side direction so that the electrodewidth in the center along the long-side direction (length along theshort-side direction) is short and becomes long at both ends along thelong-side direction. With such a configuration, the electrode 381 isformed in the entire region of the same sign (“−” sign), in which thedistortion difference DrXY is large. Therefore, the output voltagesensitivity to pressing in the surface wall 812F of the casing 810 canbe made higher.

Although FIG. 25 illustrates the example of disposing the piezoelectricsheet 380 on the almost entire face, a piezoelectric sheet having thesame shape as that of the electrode 380 may be disposed. In this case,it is sufficient to cut out a piezoelectric sheet so that, when thepiezoelectric element is disposed in the casing 810, the uniaxialstretch direction of the piezoelectric sheet forms an angle of about 45°with respect to the long-side direction and the short-side direction ofthe casing 810.

Further, as illustrated in FIG. 26, more electrodes may be formed. FIG.26 is a plan view of the casing 810, illustrating an example of adheringthe piezoelectric sheet 380 in an almost entire face of the casing 810and forming a plurality of electrodes.

A piezoelectric element 38A is obtained by adding electrodes 3821 and3822 to the piezoelectric element 38. The electrode 3821 is formed in acenter part in the long-side direction of the piezoelectric sheet 380and near one end in the short-side direction (region close to thelong-side-direction side wall 821). The electrode 3822 is formed in acenter part in the long-side direction of the piezoelectric sheet 380and near the other end along the short-side direction (region close tothe long-side-direction side wall 822). The electrodes 3821 and 3822 arenot connected to the electrode 381. Although not illustrated, also onthe face opposed to the piezoelectric sheet 380 of the electrodes 3821and 3822, electrodes having the same shape are formed.

In the case of such a configuration, the sign of charges generated bythe electrodes 3821 and 3822 is opposite to that of charges generated inthe electrode 381 (the polarities of charge distributions are opposite).Therefore, if the charges are simply added, the total amount of thecharges decreases. That is, when the voltage generated by the electrode3821 and the voltage generated by the electrode 381 are simply added,the voltage decreases. Therefore, in the case of such a configuration,it is sufficient to provide a configuration of adding the voltagesobtained by the electrodes 3821 and 3822 and the voltage obtained by theelectrode 381 without cancelling them out (the voltages are added in astate where the polarities are the same). With such a configuration, thearea of detecting charges is widened, and the output voltage sensitivitycan be made higher.

In the embodiment of the operation device, the example of detectingpressing in the surface wall has been described. The invention can bealso used for detecting pressing in the rear face wall.

In the diagrams, the dimensional relations are exaggerated forexplanation. For example, in the sectional view of the stack body, thethickness of each of parts is not limited to the ratio illustrated inthe diagram. The design can be properly changed within the range of thetechnical idea of the present invention.

DESCRIPTION OF REFERENCE SYMBOLS

-   -   10, 10A, 10B, 10C, 10D, 60: DISPLACEMENT SENSOR    -   20: ELASTIC MEMBER    -   30, 31, 32, 33, 34, 35, 36, 37, 38, 38A, 431, 432, 512:        PIEZOELECTRIC ELEMENT    -   300, 310, 320, 330, 340, 350, 360, 370, 380, 4310, 4320, 5120:        PIEZOELECTRIC SHEET    -   301, 302, 311, 312, 321, 322, 331, 341, 351, 352, 361, 362, 371,        372, 381, 3821, 3822, 4311, 4312, 4321, 4333: ELECTRODE    -   41, 42, 41A, 42A, 41B, 42B: EXTERNAL CONNECTION TERMINAL    -   100: DISPLACEMENT DETECTING DEVICE    -   101: DC VOLTAGE DETECTOR    -   201: GAME CONTROLLER    -   210: CASING    -   211: SPACE    -   220, 230: OPERATION INPUT BUTTON    -   301: SHOE WITH MONITORING FUNCTION    -   301: SHOE BODY    -   311: SOLE    -   131: COMMUNICATION CONTROL UNIT    -   132: BATTERY    -   134: POWER SUPPLY LINE    -   135: WIRING LINE    -   400: FOOT    -   401, 401A: REMOTE CONTROLLER    -   410: CONTROL CIRCUIT PART    -   420, 420D, 420U: ELASTIC MEMBER    -   440, 440A, 514: INSULATING PROTECTION LAYER    -   450: SOLAR BATTERY    -   501: TOUCH PANEL SENSOR    -   511: TOUCH PANEL PART    -   5111, 5112: CAPACITANCE DETECTING ELECTRODE    -   5121, 5122: PRESS FORCE DETECTING ELECTRODE    -   513: INSULATING LAYER    -   601: ELASTIC MEMBER    -   602: DISPLACEMENT DETECTION ELECTRODE    -   701: DEVICE HAVING FLAT PLATE SHAPE    -   720: MAIN BODY    -   731A, 731B: PIEZOELECTRIC ELEMENTS    -   801: OPERATION DEVICE    -   810: CASING    -   811: INTERNAL SPACE    -   812F: SURFACE WALL    -   812R: REAR FACE WALL    -   821, 822: LONG-SIDE-DIRECTION SIDE WALL    -   823, 824: SHORT-SIDE-DIRECTION SIDE WALL

1. A displacement sensor comprising: an elastic member; and aflat-film-shaped piezoelectric element attached to a first main face ofthe elastic member, the piezoelectric element including a pair ofopposed electrodes and a piezoelectric sheet therebetween, wherein thepiezoelectric sheet contains polylactic acid and was stretched at leastin a uniaxial direction thereof.
 2. The displacement sensor according toclaim 1, wherein the piezoelectric sheet is a substantiallyrectangular-shaped flat film, and wherein a stretch axis of the uniaxialdirection is oriented along at least a direction of about 45° or adirection of about −45° with respect to a long-side direction of thesubstantially rectangular-shaped flat film.
 3. The displacement sensoraccording to claim 1, wherein the piezoelectric sheet is a substantiallyrectangular-shaped flat film, and wherein a stretch axis of the uniaxialdirection is oriented along at least a direction of about zero degree ora direction of about 90° with respect to a long-side direction of thesubstantially rectangular-shaped flat film.
 4. The displacement sensoraccording to claim 1, wherein the piezoelectric sheet is a substantiallyrectangular-shaped flat film, and wherein a stretch axis of the uniaxialdirection is oriented along at least a direction of about 22.5° or adirection of about 67.5° with respect to a long-side direction of thesubstantially rectangular-shaped flat film.
 5. The displacement sensoraccording to claim 1, wherein the flat-film-shaped piezoelectric elementattached to the first main face of the elastic member is a firstflat-film-shaped piezoelectric element, the displacement sensor furthercomprising: a second flat-film-shaped piezoelectric element attached toa second main face opposed to the first main face of the elastic member,the second piezoelectric element including a pair of opposed electrodeswith a piezoelectric sheet therebetween, and the piezoelectric sheet ofthe second flat-film-shaped piezoelectric element contains polylacticacid and was stretched at least in a uniaxial direction thereof.
 6. Thedisplacement sensor according to claim 5, wherein the piezoelectricsheet of the first flat-film-shaped piezoelectric element is asubstantially rectangular-shaped first flat film, and wherein a stretchaxis of the uniaxial direction is oriented along at least a direction ofabout 45° or a direction of about −45° with respect to a long-sidedirection of the substantially rectangular-shaped first flat film, andthe piezoelectric sheet of the second flat-film-shaped piezoelectricelement is a substantially rectangular-shaped second flat film, andwherein a stretch axis of the uniaxial direction is oriented along atleast a direction of about zero degree or a direction of about 90° withrespect to a long-side direction of the substantially rectangular-shapedsecond flat film.
 7. The displacement sensor according to claim 5,wherein the piezoelectric sheet of the first flat-film-shapedpiezoelectric element is a substantially rectangular-shaped first flatfilm, and wherein a stretch axis of the uniaxial direction is orientedalong at least a direction of about 22.5° or a direction of about 67.5°with respect to a long-side direction of the substantiallyrectangular-shaped first flat film, and the piezoelectric sheet of thesecond flat-film-shaped piezoelectric element is a substantiallyrectangular-shaped second flat film, and wherein a stretch axis of theuniaxial direction is oriented along at least a direction of about 22.5°or a direction of about 67.5° with respect to a long-side direction ofthe substantially rectangular-shaped second flat film.
 8. Thedisplacement sensor according to claim 5, wherein the elastic member hasconductivity, and an electrode on the elastic member side of the firstflat-film-shaped piezoelectric element and an electrode on the elasticmember side of the second flat-film-shaped piezoelectric element areshared by the elastic member having conductivity.
 9. The displacementsensor according to claim 1, wherein the displacement sensor comprises astacked plurality of the flat-film-shaped piezoelectric elements. 10.The displacement sensor according to claim 5, wherein the displacementsensor comprises a stacked plurality of at least one of thepiezoelectric sheet of the first flat-film-shaped piezoelectric elementor the piezoelectric sheet of the second flat-film-shaped piezoelectricelement.
 11. The displacement sensor according to claim 1, wherein thepair of electrodes and the elastic member are translucent.
 12. Adisplacement sensor comprising: a columnar shaft; and a flat-film-shapedpiezoelectric element attached to a circumferential face of the columnarshaft the piezoelectric element including a pair of opposed electrodesand a piezoelectric sheet therebetween, wherein the piezoelectric sheetcontains polylactic acid and wherein a stretch axis is oriented ineither a direction of about zero degree or in a direction of about 90°with respect to a circumferential direction thereof.
 13. A displacementsensor comprising: first and second flat-film-shaped piezoelectricelements, each comprising a pair of opposed electrodes and apiezoelectric sheet therebetween, wherein the first and the secondflat-film-shaped piezoelectric elements have the same strength, thefirst and second flat-film-shaped piezoelectric elements are in contactwith each other so that their respective flat faces are opposed to eachother, and each piezoelectric sheet contains polylactic acid and wasstretched at least in a uniaxial direction thereof.
 14. A displacementdetecting device comprising: the displacement sensor according to claim1; a voltage measuring circuit which detects generated voltage in thedisplacement sensor; and a capacitor connected in parallel to thedisplacement sensor.
 15. An operation device comprising: a casingconfigured to be deformed when subject to an external force; adisplacement sensor which detects a displacement in a desired directionwhen the casing is deformed by the external force; and an applicationexecuting unit which executes a predetermined application in response toa detection voltage of the displacement sensor according to the externalforce.
 16. The operation device according to claim 15, wherein adisplacement in the desired direction is a displacement in a bendingdirection and/or a displacement in a twisting direction.
 17. Theoperation device according to claim 15, wherein the applicationexecuting unit comprises: a communication control unit which transmitsthe detection voltage by radio; and a program executing unit whichreceives a radio signal from the communication control unit and uses thedetection voltage for a program execution status of the application. 18.The operation device according to claim 15, wherein the displacementsensor has a flat-film-shaped piezoelectric element, the piezoelectricelement including a pair of opposed electrodes and a piezoelectric sheettherebetween, and is configured to output a detection voltage of theflat-film-shaped piezoelectric element according to a displacement. 19.The operation device according to claim 18, wherein the piezoelectricsheet contains polylactic acid and was stretched at least in a uniaxialdirection thereof.
 20. The operation device according to claim 15,further comprising a photovoltaic element in the casing.
 21. Theoperation device according to claim 18, wherein the flat-film-shapedpiezoelectric element is a first flat-film-shaped piezoelectric element,the displacement sensor further comprising: a second flat-film-shapedpiezoelectric element, the second flat-film-shaped piezoelectric elementincluding a pair of opposed electrodes and a piezoelectric sheettherebetween, and configured to output a second detection voltage of thesecond flat-film-shaped piezoelectric element according to adisplacement; and an elastic structure between the first and secondflat-film-shaped piezoelectric elements, the elastic structurecomprising: a first flat-plate-shaped elastic member; a secondflat-plate-shaped elastic member; and a photovoltaic element having aflat plate shape disposed between the first and second flat-plate-shapedelastic members, wherein the first flat-plate-shaped elastic member andthe first flat-film-shaped piezoelectric element are disposed on awave-receiving-face side of the photovoltaic element, and the firstflat-plate-shaped elastic member and the first flat-film-shapedpiezoelectric element have translucency.
 22. The operation deviceaccording to claim 20, further comprising a secondary battery thatcharges based on an electromotive force generated by the photovoltaicelement.
 23. The operation device according to claim 22, wherein thephotovoltaic element is connected to an output terminal of theflat-film-shaped piezoelectric element, and is configured to charge thesecondary battery using the detection voltage of the flat-film-shapedpiezoelectric element.
 24. An operation device comprising: aflat-film-shaped piezoelectric element having a piezoelectric sheetcontaining polylactic acid and that was stretched at least in a uniaxialdirection, and electrodes on both main faces of the piezoelectric sheet;and a casing having faces extending in two directions which aresubstantially orthogonal to each other in a plan view, wherein a regionin which the electrodes of the flat-film-shaped piezoelectric elementare opposed to each other corresponds to a position where a differenceof respective distortions is greatest when the faces extending in thetwo directions are deformed.
 25. The operation device according to claim24, wherein the piezoelectric sheet is disposed only in the region inwhich the electrodes of the flat-film-shaped piezoelectric element areopposed to each other.
 26. The operation device according to claim 24,wherein the electrodes of the flat-film-shaped piezoelectric element aredisposed in regions except for a center of planes extending in the twodirections.
 27. The operation device according to claim 24, wherein theelectrodes are disposed in a region in which polarities of chargedistributions generated by distortion of the casing are the same. 28.The operation device according to claim 24, wherein the electrodes are aplurality of partial electrodes, and the plurality of partial electrodesare connected so that polarities of voltages generated match and areadded.
 29. An operation device comprising: a flat-film-shapedpiezoelectric element having a piezoelectric sheet containing polylacticacid and that was stretched at least in a uniaxial direction, and havingpress force detecting electrodes on both main faces of the piezoelectricsheet; and a flat-plate-shaped touch panel arranged such that a mainface thereof is parallel to the flat-film-shaped piezoelectric element.